This invention relates to the separation of light particles from heavy particles in a stream of particulate matter. In particular, this invention relates to the separation of stems from tobacco filler in a cigarette maker.
In the manufacture of cigarettes, tobacco filler is produced by essentially shredding, as by multiple slitting, cured tobacco leaf. The whole leaf contains stems and large veins which are undesirable in cigarette filler because they burn unevenly and may protrude through the cigarette wrapper. Thus, care is taken to try to remove as much of the stems and veins as possible before the leaf is cut. After cutting, additional steps are taken to remove any stems and veins that may remain in the cut filler. However, some fraction of the stems and veins remain as the filler is transported to the cigarette maker.
Tobacco filler is introduced into conventional cigarette makers in a section referred to as the chimney, in which it falls against a rising current of air which carries it upwards to a perforated tape, usually steel, to which suction is applied from above. The tape continually moves horizontally, carrying the accumulated filler to subsequent sections of the cigarette maker.
It is known to provide for separation of stems and other heavy particles from the filler in the chimney. For example, it is known to provide a separation chamber below the chimney and to introduce the filler horizontally at the top of the separation chamber. A current of air rises through the separation chamber and into the chimney, carrying with it primarily light particles, although a small proportion of heavy particles are carried upwards as well. The remaining heavy particles, and some light particles, fall downward through the separation chamber. Some of the light particles slow and reverse direction as they travel against the direction of the air stream in the separation chamber, eventually rising into the chimney. The remaining light particles and the heavy particles exit at the bottom of the separation chamber. However, such systems allow some heavy particles to enter the chimney, and also allow some desirable light particles to be rejected.
It would be desirable to be able to provide a method and apparatus for separating heavy particles from a stream of particulate matter without separating any significant amount of light particles, and especially a method and apparatus for separating stems from tobacco filler in a cigarette maker.